Summary

Over the past 25 years, life expectancy has been rising in the United States at a slower pace than has been achieved in many other high-income countries. Consequently, the United States has been falling steadily in the world rankings for level of life expectancy, and the gap between the United States and countries with the highest achieved life expectancies has been widening. International comparisons of various measures of self-reported health and biological markers of disease reveal similar patterns of U.S. disadvantage. The relatively poor performance of the United States with respect to achieved life expectancy over the recent past is surprising given that it spends far more on health care than any other nation in the world, both absolutely and as a percentage of gross national product. Motivated by these concerns, the National Institute on Aging requested that the National Research Council convene a panel of leading experts to clarify patterns in the levels and trends in life expectancy across nations, to examine the evidence on competing explanations for the divergent trends, and to identify strategic opportunities for health-related interventions to narrow this gap.

PATTERNS OF MORTALITY AT OLDER AGES

To examine trends in life expectancy, the panel chose to rely on data available from the Human Mortality Database. The panel examined trends in life expectancy at birth by year for males and females in the United States and compared them with trends in other high-income countries where the data were considered to be of sufficiently high quality. For U.S. males, life expectancy at birth increased by 5.65 years from 69.99 years in 1980 to

75.6 years in 2007, the equivalent of 2.1 years per decade. While this is a significant achievement, it is less than the average increase for the other 21 countries examined for this study. Similarly, between 1980 and 2007, life expectancy at birth for U.S. women increased 3.3 years from 77.5 to 80.8 years, only slightly more than 60 percent of what was achieved, on average, in the same period in the other 21 countries examined. Among high-income countries that have recorded reductions in adult mortality at advanced ages, the Netherlands and Denmark stand out as the only other two countries that have recently underachieved. For both men and women, the divergence of experience between the United States and the other countries examined is clear both before and after age 50, although it is starker for women than for men. However, because 94–96 percent of newborns in high-income countries now survive to age 50, variation in life expectancy at birth is dominated by what happens over age 50, and the panel therefore chose to concentrate on mortality in this older age group.

The panel undertook a careful examination of cause-of-death statistics to see whether specific causes of death could account for the low level of life expectancy in the United States and were associated with improvements in life expectancy in vanguard countries. Comparative analyses of this sort are complicated by issues of variation in coding practices across countries and over time. Nevertheless, it does appear that higher mortality rates for lung cancer and respiratory diseases in the United States, Denmark, and the Netherlands are an important part of the story of recent trends. About half the gap between the United States and the countries with the highest life expectancies results from differences in mortality due to heart disease, so this condition should be a focus of efforts to bring U.S. life expectancy in line with that of the exemplar countries. Other conditions that account for the poor performance of U.S. women in particular include cerebrovascular conditions (primarily stroke), diabetes, and mental disorders.

EVIDENCE ON POSSIBLE COMPETING EXPLANATIONS

The panel examined a number of possible risk factors and considered how differentials among countries in exposure to these risk factors might account for observed disparities in levels of and improvements in life expectancy. For some factors, comparable cross-country data exist on the current levels of risk, while for others, surprisingly little direct evidence can be brought to bear. The fluid nature of the relationship between mortality and some of the major risk factors also complicated the panel’s work. For example, the epidemiological literature still reflects considerable differences of opinion with respect to the magnitude of the relationship between obesity and mortality.

The panel’s strategy was to try to establish the strength of the evidence for a number of the most commonly proffered explanations of why the

United States fares poorly on life expectancy relative to other countries—for example, that these differences are the result of a particularly inefficient U.S. health care system or that they are a function of poor health behaviors in the United States, particularly with respect to smoking, overeating, and failing to exercise sufficiently. The panel also considered differences among countries in levels of social integration and in socioeconomic inequality. Ultimately, all of these potential risk factors will need to be examined in an integrated framework across the entire life course, taking account of the effects of differences in socioeconomic status, behavioral risk factors, and social policy, as well as changing effects across particular cohorts and periods.

Smoking appears to be responsible for a good deal of the divergence in female life expectancy. Other factors, such as obesity, diet, exercise, and economic inequality, also have likely played a role in the current gap and divergence between the United States and other countries. Fifty years ago, smoking was much more widespread in the United States than in Europe or Japan: a greater proportion of Americans smoked and smoked more intensively than was the case in other countries. The health consequences of this behavior are still playing out in today’s mortality rates. Over the period 1950–2003, the gain in life expectancy at age 50 was 2.1 years lower among U.S. women compared with the average of nine other high-income countries (5.7 vs. 7.8 years gained, respectively). The damage caused by smoking was estimated to account for 78 percent of the gap in life expectancy for women and 41 percent of the gap for men between the United States and other high-income countries in 2003. Smoking also has caused significant reductions in life expectancy in the Netherlands and Denmark, which as noted are two other countries with relatively poor life expectancy trends.

Other factors, particularly the rising level of obesity in the United States, also appear to have played a significant part, although as noted, there is still a good deal of uncertainty in the literature regarding the mortality consequences of obesity and possible trends therein. Obesity may account for a fifth to a third of the shortfall of life expectancy in the United States relative to the other countries studied. Other specific risk factors also are surely important, but their effects are even more difficult to quantify. The panel found some evidence to suggest that adults aged 50 and over in the United States are somewhat more sedentary than those in Europe, but the research base is insufficient even to identify a reasonable range of uncertainty in estimates of the contribution of physical activity to international differences or trends in mortality.

In other cases, the panel determined that certain risk factors are unlikely to have played a major role in the divergence of life expectancy in various countries over the past 25 years. A large body of work shows a causal relationship between social ties and social integration and mortality. Yet there

is little basis for concluding that levels or trends in the quality of social networks have played a role in the divergent life expectancies studied. Similarly, little evidence supports the hypothesis that hormone therapy played a part in an emergent longevity shortfall for American women.

Finally, the panel examined whether differences in health care systems across countries might help explain the divergence in life expectancy over the past 25 years. The health care system in the United States differs from those in other high-income countries in a number of ways that conceivably could lead to differences in life expectancy. Certainly, the lack of universal access to health care in the United States has increased mortality and reduced life expectancy. However, this is a smaller factor above age 65 than at younger ages because of Medicare entitlements. For the main causes of death at older ages—cancer and cardiovascular disease—available indicators do not suggest that the U.S. health care system is failing to prevent deaths that would elsewhere be averted. In fact, cancer detection and survival appear to be better in the United States than in most other high-income countries. Survival rates following a heart attack also are favorable in the United States.

Most of the comparative data the panel reviewed relate to the performance of the U.S. health care system relative to those of other high-income countries after a disease has already developed. A separate concern is that the U.S. health care system does a particularly poor job at prevention, an observation that may be especially relevant in the midst of a nationwide obesity epidemic. The panel reviewed scattered evidence on the performance of the United States with respect to preventive medicine relative to European countries and found the evidence to be inconclusive. Certainly the high prevalence of certain health conditions in the United States is consistent with a failure of preventive medicine. But it could also be consistent with a higher prevalence of smoking, obesity, and physical inactivity among Americans, or with a medical system that may be unusually effective at identifying certain diseases.

LOOKING TO THE FUTURE

What will happen to life expectancy rates in the United States and other countries in the coming decades? Although it is impossible to answer that question with any certainty, the analyses described in this report point to some likely patterns for the future. Because there appears to be a lag of two to three decades between smoking and its peak effects on mortality, one can predict how smoking will affect life expectancy in various countries over the next 20 to 30 years. On this basis, life expectancy for men in the United States is likely to improve relatively rapidly in the coming decades in response to changes that have occurred in smoking patterns over the past 20 years. For

women, mortality improvements are likely to remain slower than males for the next decade or so. Similarly, life expectancy in Japan can be expected to improve less rapidly than it otherwise would because of the rapid increase in the prevalence of smoking in that country. On the other hand, the United States has been in the vanguard of a global obesity epidemic, and obesity also appears to be an important contributor to the shortfall in life expectancy in the United States. If the obesity trend in the United States continues, it may offset the longevity improvements expected from reductions in smoking. However, recent data on obesity for the United States suggest that its prevalence has leveled off, and some studies indicate that the mortality risk associated with obesity has declined. The interplay between obesity levels and obesity risks bears watching as an important factor in future longevity trends in the United States.

RESEARCH AND POLICY IMPLICATIONS

While the panel believes it made progress in identifying some of the main factors that have been driving differences in life expectancy among wealthy countries, it also identified many research gaps. With respect to behavioral risk factors, a reliable marker of the damage from smoking exists—mortality rates from lung cancer. No such clear-cut and widely available marker has been identified for obesity, physical inactivity, stress, lack of social integration, or the other risks considered in this report. Furthermore, evaluation of the importance of these risks is based primarily on observational studies that follow forward people with differing levels of exposure. These studies are subject to many biases, especially those associated with omitted variables, self-selection into categories, and reverse causation. Without randomized controlled trials, it is difficult to overcome these problems that plague observational studies. While it is sometimes difficult, expensive, and ethically challenging to alter individual behavior, there is no perfect substitute for such trials. On the other hand, studies that take advantage of natural experiments, such as increased cigarette taxes or a dramatic change in the use of hormone therapy, can sometimes serve as valuable supplements to randomized controlled trials.

The panel concluded that a history of heavy smoking and current levels of obesity are playing a substantial role in the relatively poor longevity performance of the United States. Yet these behaviors are products of a broad social and economic context encompassing, for example, a level of affluence that supports large numbers of automobiles, low taxes on gasoline, and dispersed residences and workplaces that encourage driving; a climate and soil in part of the country that are conducive to growing tobacco; a productive agricultural sector that produces inexpensive foods; and a public health system that is highly dispersed and thus heavily dependent on regional rather

than national resources. It is also true that these contextual factors are not randomly distributed in the population; rather, they are more likely to affect the health of people of lower social status and those who are less likely to have lifetime access to health care. Finally, the panel did not undertake any analysis of the cost-effectiveness of public interventions designed to change personal health behaviors; therefore, recommendations as to what might be undertaken in this regard are not appropriate. It is clear, however, that failures to prevent unhealthy behaviors are costing Americans years of life compared with their counterparts in other wealthy countries.

During the last 25 years, life expectancy at age 50 in the United States has been rising, but at a slower pace than in many other high-income countries, such as Japan and Australia. This difference is particularly notable given that the United States spends more on health care than any other nation. Concerned about this divergence, the National Institute on Aging asked the National Research Council to examine evidence on its possible causes.

According to Explaining Divergent Levels of Longevity in High-Income Countries, the nation's history of heavy smoking is a major reason why lifespans in the United States fall short of those in many other high-income nations. Evidence suggests that current obesity levels play a substantial part as well. The book reports that lack of universal access to health care in the U.S. also has increased mortality and reduced life expectancy, though this is a less significant factor for those over age 65 because of Medicare access. For the main causes of death at older ages -- cancer and cardiovascular disease -- available indicators do not suggest that the U.S. health care system is failing to prevent deaths that would be averted elsewhere. In fact, cancer detection and survival appear to be better in the U.S. than in most other high-income nations, and survival rates following a heart attack also are favorable.

Explaining Divergent Levels of Longevity in High-Income Countries identifies many gaps in research. For instance, while lung cancer deaths are a reliable marker of the damage from smoking, no clear-cut marker exists for obesity, physical inactivity, social integration, or other risks considered in this book. Moreover, evaluation of these risk factors is based on observational studies, which -- unlike randomized controlled trials -- are subject to many biases.

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